*{
    padding: 0;
    margin: 0;
}
.wn{
    width: 1200px;
    margin:100px auto;

}
.wn1{
    width: 33.3333333%;
    background: red;
    float: left;
    height: 100px;
    text-align: center;
}
.wn::after{
    content: "";
    display: block;
    clear: both;
}

/*响应式样式*/
@media (max-width:600px) {
    .wn{
        width: 100%;
    }
    .wn1{
        width: 100%;
        background: blue;
        color: #ffffff;
    }
}